It is generally accepted in the scientific community that genes play a role in animal development and that the regulation of gene expression plays a key role in the development of some diseases or conditions that affect an animal's health and well being. Similarly, the differential expression of genes is one factor in the development of such diseases and conditions and the evaluation of gene expression patterns has become widely recognized as crucial to understanding the development and control of such diseases and conditions at the molecular level. To advance the understanding of genes and their relationship to disease, a number of methods have been developed for studying differential gene expression, e.g., DNA microarrays, expressed tag sequencing (EST), serial analysis of gene expression (SAGE), subtractive hybridization, subtractive cloning and differential display (DD) for mRNA, RNA-arbitrarily primed PCR (RAP-PCR), Representational Difference Analysis (RDA), two-dimensional gel electrophoresis, mass spectrometry, and protein microarray based antibody-binding for proteins.
Virtually all joints in the body of a mammal have cartilage. Cartilage is the supporting structure of the body and consists of thick bundles of fibrous protein (collagen) which are woven to form an articular surface. Proteoglycans fill extracellular spaces not occupied by collagen. Such proteoglycans are comprised of a combination of a protein and a sugar. Each proteoglycan subunit contains a protein core consisting of long chains of modified sugars known as glycosaminoglycans (GAGs). Glucosamine is the single most important component and precursor for GAGs. Synthesis of collagen by the body is dependent upon GAG synthesis. Chondrocytes in the cartilage utilize glucosamine to produce N-acetylglucosamine (NAG) and glucuronic acid, which are utilized by the body to form hyaluron. Hyaluron confers a lubricating property to the joint of the animal's body.
Cartilage is important in the body of animals for providing flexibility, compressibility under pressure, cushion, tensile strength, range of motion and smoothness of movement within joints. Examples of joints having cartilage include fingers and toes, neck, knee, hip, shoulder and the like. Animals can suffer from a number of conditions where cartilage is degraded thereby bringing about a reduction in the joint's flexibility, compressibility and often times resulting in a generalized inflammation of the joint and/or tissue surrounding the joint and in some cases the development of conditions such as osteoarthritis and rheumatoid arthritis. Such animals then have significant loss of joint function and experience pain.
Arthritis is a musculoskeletal disorder. Osteoarthritis is the most common type of arthritis in animals and humans. Osteoarthritis is a degenerative joint disease commonly occurring in humans and companion animals and the disease is characterized by degenerative changes in the articular cartilage, with loss of proteoglycan and collagen and proliferation of new bone formation at articular margins. These changes are accompanied by a variable inflammatory response within the synovial membrane. A principal defect in hyaline cartilage at the articular surface of a joint is the alteration in the ratio of glycosaminoglycans to the collagen fiber content of the matrix. Bones directly underlying cartilage in the joints are called subchondral bones. These subchondral bones nourish the overlying cartilage which itself is devoid of blood vessels, nerves or lymphatic tissue.
A natural erosion of cartilage occurs with age, but may also result from excessive loads placed on joints, obesity, heredity, trauma, decreased circulation, poor bone alignment and repetitive stress may exacerbate the condition of the joint. It is postulated that free radical damage may contribute to the development of osteoarthritis.
Cells of hyaline cartilage known as chondrocytes produce and maintain the surrounding extracellular matrix. Maintenance of homeostatis of the cartilage matrix depends upon catabolism of matrix proteins such as type II collagen and aggrecan. These proteins are digested and replaced by new proteins synthesized by chondrocytes. Catabolism is in part carried out by proteolytic enzymes such as matrix metalloproteinase (MMP) and aggrecanase proteins. In a normal animal, a balance is achieved between synthesis and degradation, thereby maintaining healthy cartilage. When the balance shifts to degradation, pathogenesis ensues and may result in joint inflammation and osteoarthritis.
A homeostatic condition in cartilage is dependent upon regulation through intercellular signaling between chondrocytes. Chondrocytes thus produce and respond to signaling molecules. Such signaling molecules may comprise cytokines and growth factors which may directly influence cellular metabolism. Intercellular signaling is complex and has not been fully characterized. Growth factor molecules such as TGF-beta are involved and believed to promote type II collagen production and to, inhibit collagen cleavage. Cytokines, such as TNF-alpha and IL-1-beta, also play a role. These cytokines are believed to promote production of proteases that may degrade cartilage. Numerous other complex interactions are believed to be occurring as a result of intercellular signaling.
Due to the complexity of the intercellular signaling process, it is highly desirable to understand at a genetic level the interactions that are taking place. Detection of dysregulated genes in a pre-arthritic or an arthritic condition is helpful in understanding the biology of abnormal musculoskeletal joint disorders, especially on a genome-wide basis. A more detailed understanding of the biological pathways involved through gene expression profiling will aid in the development of salutary pharmaceutical, nutraceutical and nutritional (dietary) interventions in the disease pathways. These approaches may enable prevention, early detection and treatment of the underlying abnormal musculoskeletal joint conditions as well as in monitoring the prognosis of such abnormal musculoskeletal joint disorders, especially in osteoarthritis. Dysregulated genes involved in the pathology of such disorders may serve as important biomarkers to optimize selection of appropriate pharmaceutical, nutraceutical and nutritional (dietary) interventions.
There is yet to be identified a drug that reverses the course of osteoarthritis. Currently available therapeutic agents are employed to reduce inflammation and/or to relieve pain. Current therapy employs a class of drugs known as non-steroidal anti-inflammatory drugs (NSAIDs) to treat musculoskeletal joint disorders such as osteoarthritis, but these therapies have a variety of drawbacks, including, in particular, gastrointestinal disorders and they may also inhibit cartilage formation.
Large dogs may develop arthritis as they age. Large dog breeds are more susceptible to arthritis due to their increased mass and/or genetic disposition. Large dogs are not the only animals at risk of arthritis and other cartilage conditions. Arthritis and other degenerative joint diseases have been commonly recognized in dogs and such conditions have been shown to be prevalent in cats. Feline osteoarthritis is a disease primarily affecting aged felines ten years of age or older. Animals at risk of developing cartilage-affecting abnormal musculoskeletal joint disorders include, but are not limited to, mammals such as canine, feline, equine, hircine, ovine, porcine, bovine, human and non-human primate species, and birds including turkeys and chickens.
Diet plays an important role in disease causation and progression because it is fundamentally involved in metabolism. Disease regulated genes are at some level regulated by nutritional factors. Thus, dietary components present in foods as nutrients may regulate gene expression at the transcriptional and translational level, as well as in certain post-translational modifications. They may similarly be involved in degradation and enzymatic activities. Nutrient levels may influence the equilibrium of metabolic pathways. Metabolic pathways are frequently complex and may involve many redundancies and interrelationships among different metabolic pathways. Altering the concentration of a single enzyme, growth factor, cytokine or metabolite may impact a number of metabolic pathways involved in disease-related physiology. Hormones and other cell signaling molecules are well-understood to be regulated by diet and are also known to be implicated in the development and progression of disease.
The same disease phenotype may result from disturbances in different metabolic pathways, and the genetic make-up of each animal differs, thereby causing variation in responses to the same factors, including nutritional and environmental factors. The interplay of genetic, nutritional and environmental factors is important in understanding the etiology, prevention, treatment and progression of diseases in animals. Finding gene expression responses to nutrients associated with various diseases and disorders permits formulation of diets for animals susceptible to disease such as abnormal musculoskeletal joint disorders, and further permits diagnosis, treatment and monitoring the prognosis of the underlying disease.
Nutritional components influence gene expression, including mRNA production (transcription), mRNA processing, protein production (translation) and post-translational modifications, thereby influencing the overall metabolic status of an animal. As a result, the use of biomarkers for early detection and monitoring of disease progression and/or genotype-based diets may enable prevention or treatment of diseases as well as new therapies to be developed for animals, particularly for companion animals. Diet is arguably the most important environmental factor affecting the phenotype of an animal, including susceptibility to disease.
Gene expression may be regulated through unstable processes that are controlled by activators and repressors of gene function. Nutritional status may cause significant changes in gene transcription rates. Macronutrients such as glucose, fatty acids and amino acids and micronutrients such as iron, zinc and vitamins can regulate gene expression. Various bioactive food components such as carotenoids, flavonoids, monoterpenes and phenolic acids may act as transcription factors affecting gene expression. These substances tend to have direct effects on gene expression. In other situations, substances like dietary fiber, which is fermented in the gut by bacteria, may lead to the production of nutrients such as short chain fatty acids. Such substances may act as indirect activators or repressors of gene expression.
Identification of nutrient-related changes upon transcription and translation may be detected in experiments of the type described in this specification. In view of the extensive array of genes profiled in the examples of this specification, alterations in gene expression and quantification are readily detected by the methods taught in this specification. Thus, dietary and metabolic gene expression signatures may be readily ascertained using the techniques taught in the Examples of this specification. Biomarkers of the invention are proteins and/or nucleic acids that are differentially expressed in animals. Biomarker expression can be assessed at the protein or nucleic acid level using various methods known to the skilled artisan.
Only very limited work has been done to date in screening the canine and feline genomes for gene expression profiles in response to nutritional components in the diet of these companion animals. Work has been done in the area of cancer employing a canine gene microarray for CG analysis of tumors. Thomas R. et al. A canine cancer gene microarray for CGH analysis tumors, Cyrogenet. Genome Res., 2003; 102:254-260. Further works has been done in the area of dilated cardiomyopathy. Oyayma, M. A. et al., Genomic expression patterns of cardiac tissue from dogs with dilated cardiomyopathy, Am. J. Vet. Res. 2005; 66:1140-1155. To date the study of the canine genome with respect to osteoarthritis has been very limited. In one study, the MIG-6 gene was found to be elevated in dogs in the high risk osteoarthritis group and it has been hypothesized that this gene may be implicated in cartilage degradation and in the production of cartilage in dogs. Mateescu, R. G. et al., Increased MIG-6 mRNA transcipts in osteoarthritic cartilage. Biochem. Biophy. Res. Commun. 2005; 332:482-486.
Studies in healthy populations of animals versus populations having a disease such as the abnormal musculoskeletal joint disorders described in this specification have not been extensively conducted. Little data is available with respect to the canine genome and far less with respect to the feline genome. Gene expression data contained in this specification identifies genes associated with cartilage degradation in dogs and cats. Such gene expression data enables identification of nutritional compositions capable of modulating expression of such genes in a favorable manner. This is also the case with respect to genes generally associated with inflammation. Analogous data in felines is additionally set forth in the specification, figures and examples of this specification.
Gene expression data contained in the specification and examples enables a variety of desirable inventions based on the gene expression profiles described herein. The data permits identification and quantification of gene expression products as biomarkers of nutrition as well as disease prevention, identification and treatment of the underlying abnormal musculoskeletal joint disorder. Gene expression data elicited as a result of the practice of the methods of the invention also permits monitoring the progression of such abnormal musculoskeletal joint disorders. These inventions further include genetic testing to identify susceptible subpopulations of animals likely to be afflicted with such abnormal musculoskeletal joint disorders, to identify optimal diets for the prevention or treatment of such disorders, to identify pharmaceutical, nutraceutical and nutritional (dietary) interventions based on the findings set forth in this specification in order to treat the underlying diseases and inflammation. The inventions also include biomarkers for early disease detection, targeted therapeutics, diagnostic reagents and kits for the analysis of tissue and blood samples from animals susceptible to or having such abnormal musculoskeletal joint disorders.
In designing foods for animals, for example, companion animals such as cats and dogs, optimal animal health or wellness through good nutrition is an important goal. However, even the most nutritious animal food is of little value if the animal rejects or refuses to eat the food, or if the animal's intake of the food is restricted because the animal finds the food unpalatable. Thus, the inventions set forth in this specification further comprise nutritional compositions capable of promoting the health and wellness of animals susceptible to or having such abnormal musculoskeletal joint disorders. The invention thus encompasses edible food compositions for companion animals, which have therapeutic and prophylactic efficacy and possess increased palatability over currently marketed companion animal food products.